The present invention relates to nonwoven sheets, and adhesive articles made therefrom, and in particular, to nonwoven sheet materials and adhesive articles that exhibit enhanced tear characteristics.
Nonwoven sheet materials are often used as the backing or web component of tapes and the like. These tapes are commonly used in the health-care industry for affixation of a variety of articles, such as dressings and tubings, and as backings and affixation materials for pre-made dressings, such as first-aid dressings and island-type dressings. They are also commonly used as affixation materials on certain types of products, such as diagnostic electrodes, surgical grounding plates, and monitoring electrodes.
Tapes formed from nonwoven sheet materials fall into two general categories based on performance needs. Category I includes sheet materials, and tapes made therefrom, that can be torn in the cross machine or cross web direction. However, these materials often cannot be torn cleanly, and therefore, display uneven or irregular torn edges. On the other hand, category II includes those sheet materials and tapes that, for practical purposes, cannot be torn in either the down web direction or the cross web direction.
In general, category I nonwoven materials are predominantly comprised of cellulosic fibers, and exhibit a down web direction to cross web direction tensile strength ratio of less than 2.5 to 1. Cellulosic fibers are inherently fracturable (i.e., are easily broken under stress), as opposed to many synthetic, polymeric fibers, that are essentially nonfracturable.
The cellulosic fibers used in category I sheet materials are typically bonded together by a chemical binder that immobilizes, or partially immobilizes the fibers. In addition, the chemical binder increases the density of the sheet materials, and provides other advantageous properties, such as enhanced tensile strength, elongation at break, Hand (i.e., conformability), decreased fuzzing, and the specific tear characteristics noted above. However, these advantageous properties are rapidly compromised when the sheet material becomes wet, and especially when it becomes saturated with water or other water-based fluids.
Category II materials are most frequently formed from essentially nonfracturable synthetic fibers, and are either thermally, mechanically, or chemically bonded to provide structural integrity to the sheet materials. These materials can display enhanced tensile strength, elongation, Hand, and depending on their particular construction. For example, mechanically bonded category II materials are typically softer and more fuzzy, in comparison with the chemically bonded materials, that tend to be stiffer and less fuzzy. However, in virtually all instances, category II sheet materials are essentially incapable of being torn in the cross web direction, and thus, do not meet the affixation requirements of the health-care industry.
Both category I and II nonwoven sheet materials and tapes enjoy reasonably extensive use in the wound treatment and medical device affixation areas of the practice of health-care. However, neither type of material has been able to make significant advances into the broader areas of the health-care market due to their inherent limitations.
Category I materials lack water resistance, and are unable to provide sufficient strength, while still maintaining softness, Hand and/or reasonable tear characteristics. Strength can be improved by changing the down web direction to cross web direction orientation ratios of the fibers at the expense of tear. In addition, strength can also be improved by increasing the basic fiber content and weight at the expense of Hand and tear.
Altering the characteristics of category II sheet materials made with synthetic polymer fibers is even more restrictive. Reasonably good tear can only be achieved by utilizing fibers that make the sheet materials, and resulting tapes, very stiff. In so doing, the fiber-to-fiber bonds are essentially locked-up, thereby reducing fabric conformability, and providing a tear which is extremely difficult, and not satisfactory in terms of ragged edges and failure to tear straight.
Many attempts have been made in recent years to enhance the characteristics of category I and II materials, or to provide nonwoven sheet materials and tapes with the desirable characteristics of both category I and II materials. In so doing, different fiber types, contents, and weights of the nonwoven sheet materials have been tried. In addition, various bonding techniques, including bonding with a chemical sizing agent, physical entanglement of the web (e.g., hydroentanglement) and thermal bonding, such as through thermal embossing, have been employed. See, e.g., U.S. Pat. No. 4,973,513 (chemical bonding with LAB), U.S. Pat. No. 4,341,213 (chemical bonding to increase strength and flammability), U.S. Pat. No. 4,772,499 (hydroentanglement and partial chemical bonding), U.S. Pat. No. 3,737,368, and U.S. Pat. No. 3,507,943 (thermal embossing with engraved rollers).
For example, U.S. Pat. No. 3,121,021 discloses surgical adhesive tape formed from a tissue backing of rayon staple fibers coated with a non-tacky hydrophobic rubbery fiber-sizing polymer. The polymer-bonded backing is coated with a thin layer of pressure-sensitive adhesive that exhibits a microporous structure after drying. Incorporation of the hydrophobic rubbery fiber-sizing polymer serves to increase the water repellency, and thus, the wet strength of this category I material. Similarly, U.S. Pat. No. 4,112,177 provides essentially the same nonwoven backing as with U.S. Pat. No. 3,121,021, however, multiple adhesive layers are applied to the backing to improve the overall adhesive properties of the tapes formed therefrom. A further example of a porous, double-coated adhesive tape is disclosed in U.S. Pat. No. 4,844,973.
U.S. Pat. No. 4,292,360 discloses a multi-ply nonwoven sheet material that can be used to make pressure-sensitive adhesive tapes. The sheet materials are comprised of two nonwoven webs that are overlaid and bonded together by a rewettable chemical binder. The nonwoven webs can be formed of any type or combination of staple fibers, either alone, or in combination with binder fibers. In addition to the chemical binder, the sheet materials can also be optionally calendered or embossed.
U.S. Pat. No. 3,908,650 discloses a microporous tape formed from a nonwoven web coated on one side with a porous layer of a pressure-sensitive adhesive, and on the other with a porous thermoplastic film. The fibers adjacent the thermoplastic layer are, at least to some extent, water repellent. Optionally, the fibrous web may be thermally bonded or chemically bonded with a sizing agent. Utilization of the thermoplastic layer imparts increased abrasion and soil resistance to the overall tape.
U.S. Pat. No. 4,772,499 discloses a nonwoven web that is readily tearable in the cross web direction. The tearability of the web is enhanced by pattern bonding portions of the web with a bonding agent. After drying, the web is stated to be readily tearable in the cross web direction along the non-bonded portions of the web. Also, U.S. Pat. No. 4,303,724 discloses the use of texturized or false twist yarns in the filing of nonwoven fabrics to improve their tear characteristics.
German Patent No. DE 1 595 300 discloses nonwoven fabrics formed from wet-laid webs that are hot calendered while the web still retains from 10% to 40% by weight residual moisture. These webs are comprised of unstretched polyester binder fibers, and optionally can include stretched polyester fibers, polyacrylamide fibers, and/or polyamide imide fibers. Further examples of thermal bonding as the principal means of reinforcing nonwoven materials can also be found in U.S. Pat. Nos. 4,731,277, 4,639,390, 4,511,615, 4,490,427, and 4,083,913. In addition, thermal bonding can be brought about by embossing such sheet materials using heated, engraved rollers. See, e.g., U.S. Pat. Nos. 3,737,368 and 3,507,943.
U.S. Pat. No. 4,490,425 discloses a soft and fluffy nonwoven fabric formed by thermal bonding staple fibers, endless fibers, or both, and needle puncturing (i.e., tacking) one or both sides of the fabric to form the fluffy surface. Thereafter, one or more of the sides are coated with a thermal adhesive to yield a fabric useable as an interlining in various garments. Similar interlining materials and methods of their preparation are also disclosed in U.S. Pat. Nos. 4,451,314 and 4,148,958.
None of the previously described sheet materials or tapes has successfully combined the advantages of category I and II materials, while eliminating their shortcomings. In fact, to date, no single nonwoven sheet material, or tape made therefrom, exhibits enhanced strength, enhanced overtaping, and ease of tear in any direction, while maintaining reasonable Hand values.
The present invention provides nonwoven sheet materials, and tapes formed therefrom, made with fibers, preferably tensilized nonfracturable staple fibers, and binder fibers, and formed from a combination of interbonding, smooth roll calendering, and pattern embossing techniques. These sheet materials are especially useful as tape backing fabrics that are finger tearable in the cross web and the down web directions within the requirements of the user community, and also possess a number of other desirable properties, including acceptable tensile strength and enhanced overtaping, for example.
One aspect of the present invention provides a pressure-sensitive adhesive article including nonwoven backing having a first surface and a second surface; and a pressure sensitive adhesive coated on the first surface of the backing, wherein the backing comprises an embossed pattern on a first fibrous web. In accordance with the present invention, the embossed pattern is selected from the group consisting of at least two rows of a plurality of depressions in a first direction aligned to form columns of the plurality of depressions in a second direction, wherein a distance between two depressions in one column varies from a distance between two depressions in a second column, and at least two rows of a plurality of depressions in a first direction aligned to form columns of the plurality of depressions in a second direction, wherein a distance between two depressions in at least one column varies along the first direction. A pressure sensitive adhesive article according to the present invention can also include a low adhesion backsize composition coated on the second surface of the backing and/or a release liner on the pressure sensitive adhesive coated on the first surface of the backing. Typically, the pressure sensitive adhesive is selected from the group consisting of a rubber-based adhesive, a water-based adhesive, a solvent-based adhesive, a hot-melt adhesive, and a combination thereof. A pressure sensitive adhesive article in accordance with the present invention can also include a backing that further includes a second nonwoven web, preferably laminated to the first nonwoven web.
Another aspect of the present invention provides a nonwoven sheet article including an embossed pattern on a fibrous web selected from the group consisting of at least two rows of a plurality of depressions in a first direction aligned to form columns of the plurality of depressions in a second direction, wherein a distance between two depressions in one column varies from a distance between two depressions in a second column, and at least two rows of a plurality of depressions in a first direction aligned to form columns of the plurality of depressions in a second direction, wherein a distance between two depressions in at least one column varies along the first direction.
In any of the articles according to the present invention, the fibrous web preferably includes nonfracturable staple fibers, binder fibers, and a binding agent.
Preferably, the plurality of depressions is up to about 28% of a total surface area of the backing.
Each of the plurality of depressions can be in a shape selected from the group consisting of a diamond, a rectangle, a circle, an oval, a triangle, a xe2x80x9c+xe2x80x9d sign, a xe2x80x9c less than xe2x80x9d sign, a xe2x80x9c greater than xe2x80x9d sign, and a combination thereof. Preferably, the distance between two consecutive depressions in a first direction is about 0.51 mm to about 0.36 mm and the distance between two consecutive depressions in a second direction is about 0.51 mm to about 3.6 mm. Preferably, the first direction and the second direction are substantially normal to one another.
In one embodiment, each of the plurality of depressions in a row is in a shape selected from the group consisting of alternating xe2x80x9c+xe2x80x9d signs and xe2x80x9cxe2x88x92xe2x80x9d signs. In another embodiment, each of the plurality of depressions is a xe2x80x9c+xe2x80x9d sign and the plurality of depressions is about 15% to about 22% of a total surface area of the backing. In yet another embodiment, the plurality of depressions is a combination of a xe2x80x9c+xe2x80x9d sign and a xe2x80x9cxe2x88x92xe2x80x9d sign and the plurality of depression is about 15% to about 20% of a total surface area of the backing. In a further embodiment, the plurality of depressions is a combination of a xe2x80x9cxe2x88x92xe2x80x9d sign and a xe2x80x9c|xe2x80x9d such that the plurality of depressions is about 15% to about 22% of a total surface area of the backing. In yet a further embodiment, the plurality of depressions is a combination of a xe2x80x9c+xe2x80x9d sign and a xe2x80x9cxe2x88x92xe2x80x9d sign such that the plurality of depressions is about 15% to about 20% of a total surface area of the backing.
A further aspect of the present invention provides a method for making a nonwoven sheet material that includes forming a randomly interlaced fibrous web of tensilized nonfracturable staple fibers and binder fibers; pattern embossing the fibrous web with a pattern selected from the group consisting of at least two rows of a plurality of depressions in a first direction aligned to form columns of the plurality of depressions in a second direction, wherein a distance between two depressions in one column varies from a distance between two depressions in a second column, and at least two rows of a plurality of depressions in a first direction aligned to form columns of the plurality of depressions in a second direction, wherein a distance between two depressions in at least one column varies along the first direction; subsequent to pattern embossing, smooth roll calendering the fibrous web; and subsequent to smooth roll calendering, uniformly interbonding the fibrous web throughout using a chemical bonding agent.
Yet a further aspect of the present invention provides a method for making a nonwoven sheet material that includes forming a randomly interlaced fibrous web of tensilized nonfracturable staple fibers and binder fibers; first smooth roll calendering the fibrous web; pattern embossing the fibrous web with a pattern selected from the group consisting of at least two rows of a plurality of depressions in a first direction aligned to form columns of the plurality of depressions in a second direction, wherein a distance between two depressions in one column varies from a distance between two depressions in a second column, and at least two rows of a plurality of depressions in a first direction aligned to form columns of the plurality of depressions in a second direction, wherein a distance between two depressions in at least one column varies along the first direction; and uniformly interbonding the fibrous web throughout using a chemical bonding agent, wherein smooth roll calendering is performed prior to pattern embossing or uniformly interbonding. In one embodiment, uniformly interbonding is performed prior to pattern embossing. In another embodiment, pattern embossing is performed prior to uniformly interbonding.
Preferably, the interbonding step comprises infusing the fibrous web with a water-based chemical binding agent.
A method in accordance with the present invention can also include drying the fibrous web infused with the water-based chemical bonding agent until substantially all the water is removed.
Other steps that can be included in a method in accordance with the present invention include coating a layer of pressure sensitive adhesive on a first surface of the embossed pattern web, coating a low adhesion composition on a second surface of the embossed pattern web, winding the embossed pattern web in a roll such that the pressure sensitive adhesive on the first surface of the embossed pattern web contacts a low adhesion backsize on the second surface of the embossed pattern web, and a combination thereof.
Yet another aspect of the present invention provides a method of making a pressure-sensitive adhesive article including forming a first randomly interlaced fibrous web; smooth roll calendering the fibrous web; pattern embossing the fibrous web to form an embossed pattern comprising a plurality of discontinuous depressions in a first direction and a second direction; uniformly interbonding the fibrous web throughout using a chemical bonding agent; and coating a first surface of the fibrous web with a pressure sensitive adhesive, wherein the pressure sensitive adhesive article has an overtaping value of less than about 76 mm. A method may also include other steps such as laminating a second fibrous web to the first fibrous web and coating a low adhesion backsize on a second surface of the fibrous web.
In one embodiment, pattern embossing the fibrous web occurs prior to smooth roll calendering the fibrous web and uniformly interbonding the fibrous web. In another embodiment, smooth roll calendering the fibrous web occurs prior to pattern embossing the fibrous web and uniformly interbonding the fibrous web. In yet another embodiment, uniformly interbonding the fibrous web occurs prior to pattern embossing the fibrous web.
The terms xe2x80x9cmachine directionxe2x80x9d and xe2x80x9cdown web directionxe2x80x9d are used interchangeably and refer to the lengthwise direction of the web. The fibers which comprise the nonwoven sheet materials are predominantly oriented in the down web direction of the nonwoven sheet materials. The terms xe2x80x9ccross machine directionxe2x80x9d and xe2x80x9ccross web directionxe2x80x9d are used interchangeably herein and refer to a direction about perpendicular to the down web direction of the nonwoven sheet materials.
As used herein, xe2x80x9cembossed patternxe2x80x9d and xe2x80x9ccalendered patternxe2x80x9d are used interchangeably and refer to a predetermined configuration of depressions on the surface of the web. An embossed pattern is to be distinguished from a xe2x80x9cperforatedxe2x80x9d pattern, which refers to a predetermined configuration of punctures that pass through the entire thickness of the web. Thus, an embossed pattern on a web/tape backing in accordance with the present invention is a non-perforated pattern of depressions in the surface of the web, such that the pattern is preferably discontinuous in both the down web and the cross web directions.